Pressure vessels

ABSTRACT

An inflatable pressure vessel (1), which may be a decompression chamber for treating divers, has a flexible elongate casing (2) made of a silicone elastomer material reinforced with windings of reinforcing filaments and one or more removable end members (7,8) to provide access. An end member may be a rigid plate which seals against a frame (3,4) defining the entrance under internal vessel pressure. A transparent plastic plate gives illumination and allows inspection of a diver under treatment in a decompression chamber. Two pressure vessels (31,32) may be connected by a linking element (24) comprising a male part (25) which seals within a female part (33,34) under internal pressure and which has inter-engaging projections (29,35) and depressions (30,36) to prevent the parts from sliding apart axially under that pressure.

BACKGROUND OF THE INVENTION

This invention relates to pressure vessels, and particularly todecompression chambers used to protect divers suffering fromdecompression syndrome (bends). Fixed metal decompression chambers areusually located at permanent sites in hospitals and medical centres.However, since delay in treatment can worsen the condition and lead insome cases to death, portable decompression chambers have beendeveloped.

In order to reduce the weight of portable chambers still further andmake them stowable for ease of carrying in helicopters and small boats,collapsible chambers have been developed in which the chamber is aflexible bag which becomes inflated by the chamber pressure. One suchchamber, also known as a hyperbaric chamber, is described inGB-A-2,164,984.

The present invention is concerned with the construction of a pressurevessel of the type having a flexible wall and also discloses a linkingelement for connecting two pressure vessels so that, for example, adiver temporarily under treatment in a portable decompression chambercan be transferred to a fixed decompression chamber without possiblefatal loss of pressure.

SUMMARY OF THE INVENTION

According to this invention, an inflatable pressure vessel comprises anelongate casing having end members for closing the casing to form avessel of which at least one of the end members is removable to provideaccess to the interior of the vessel, the casing comprising a flexibletubular wall of a silicone elastomer material incorporating windings ofreinforcing filaments or yarns.

The inflatable pressure vessel may be a decompression chamber having acasing of a size when inflated to accommodate a recumbent person.

The tubular casing is preferably cylindrical or frusto-conical and ispreferably of circular cross-section. The removable end member (ormembers) may be a rigid plate of a shape and size corresponding to thecross-section of the inflated casing and sealingly locatable from withinthe casing against an internal frame secured to the wall of the casingand defining the open end of the casing which the end member is toclose. Thus, internal vessel pressure forces the rigid end plate againstan inwardly-facing surface of the frame to seal the vessel.

With a casing of circular cross-section, the rigid end plate may be adisc which seats against the inside surface of a ring which is fixed tothe wall of the casing around the open end or is moulded integrally withthe wall. If the compression vessel has the tubular female part of alinking element formed as an extension of the wall of the casing, thenthe frame or ring against which the rigid end plate or disc is to seatmay be located co-axially adjacent to that female part of the linkingelement between the linking element and the main body of the casing.Insertion of a rigid end member through the open end of the casing intoits interior is facilitated if the female part of the linking elementhas a degree of flexibility.

The services for the pressure vessel such as pressurising gas feeds maybe provided through one or more ports in the at least one end member orboth end members.

The at least one end member or both end members may be a rigid plate ordisc as mentioned and this is preferably of a domed shape to increaseits strength against internal pressure in the vessel. For adecompression chamber where lightness of weight is important, a plasticsmaterial may be used for the end members and this is preferablytransparent to allow illumination of the chamber and inspection of aperson contained therein. A transparent acrylic plastics material issuitable in this regard.

The material used for the construction of the casing of the inflatablepressure vessel is important. Silicone elastomer materials provide therequired combination of lightness in weight, flexibility and toughnessin use as well as being essentially non-toxic to humans and having lowflammability characteristics. All of these properties are important inrelation to portable decompression chambers in particular.

In addition, silicone elastomer materials have good processingproperties in the filament winding process used to make the casing ofthe pressure vessel. Suitable materials can be obtained as two-componentliquid resin systems which on mixing the two components yields amaterial having appropriate viscosity and pot life for a filamentwinding process and having a suitable curing cycle.

Examples of suitable silicone elastomer materials are those produced bythe General Electric Corporation under their codes SLE 5300, RTV 615 andRTV 630 and by Dow Corning Limited under their trade name Sylgard 182.For example, SLE 5300 has a viscosity on mixing of the two components of16,000 centipoises, a pot life at a temperature of 25° C. of 48 hoursand a cure cycle of 15 minutes at a temperature of 120° C. The curedelastomer has a Shore A Durometer hardness of 33. The equivalent figuresfor RTV 630 are viscosity-150,000 centipoises; pot life (25° C.)-4hours, cure cycle-1 hour at 100° C.; and a Shore Durometer hardness of65.

The casing of the pressure vessel may be formed by winding reinforcingfilaments or yarns circumferentially onto a mandrel of the appropriatesize. The reinforcing filaments may be in the form of a tow or band oryarn of filaments and may be of any suitable material such as glass orhigh strength polymers. Polyaramid filaments or yarns such as "Kevlar"(Registered Trade Mark) are preferred. The filaments or yarns may bepre-impregnated with the silicone elastomer precursor, additionalquantities of which may be applied directly onto the mandrel ifnecessary. Gel coats may be applied pre- and/or post-winding to give asmooth surface to the casing or to apply, for example, a moreabrasion-resistant inner and/or outer coating.

The winding process for the reinforcing filaments or yarns may employsuitable lay up patterns according to design requirements including hoopwindings, angled windings and cross-windings. Local reinforcement usingwoven fabrics or tapes may be introduced during winding according todesign requirements and a frame or ring for eventual location of the atleast one end member may be incorporated during or after winding.

The loading of filaments or yarns in the flexible tubular wall of thecasing may be varied to suit performance requirements. A loading of 50to 60 percent by volume, preferably about 55 percent by volume, offilaments or yarns is a suitable loading for many applications.

After winding, the silicone elastomer material may be cured by heatingit on the mandrel using, for example, an oven or radiant heat and thenthe resulting casing may be removed from the mandrel.

The winding-reinforced silicone elastomer casing has high tensilestrength and good tear strength combined with the other propertiesoutlined above. In addition, silicone elastomer materials can bepigmented without any great loss of strength or flexibility which allowssuitable colouration of the pressure vessel, for example in NavalService colours.

A linking element for connecting the respective interiors of twopressure vessels in fluid-tight relation comprises a tubular female partsealingly connected to an entry port of a first pressure vesselaccording to the invention and a tubular male part sealingly connectedor connectable to an entry port of the second pressure vessel, thetubular male part having at least part of its external surface shaped tocorrespond with at least part of the internal surface of the female partand to seal against that surface when the vessels are internallypressurised, said respective surfaces each having projections anddepressions which engage and hold the surfaces against their slidingaxially apart under internal vessel pressure. Preferably, the male andfemale parts are cylindrical in shape.

The wall defining the external surface of the male part is preferablyflexible to facilitate sealing of the corresponding surfaces againsteach other under internal vessel pressure. Flexibility also facilitatesinsertion of the male part into the position of engagement within thefemale part.

The projections and depressions are preferably a succession ofcircumferential beads and grooves of which the beads of one part engagein the grooves of the other. With this arrangement, the wall of the malepart needs to be sufficiently flexible to allow the beads on the malepart to pass within the beads on the female part during insertion of themale part into the female part.

Preferably each bead on the internal surface of the female part of thelinking element has sides with different angles of slope similar to sawteeth. In axial cross-section, the beads of the female part can havesides with different angles of slope in relation to the longitudinalaxis of the female part, with those sides of the beads which are to facetowards the entrance to the female part being steeper in slope than theopposite sides of the beads. The beads on the male part can also havesides with different angles of slope, in cross-section, in relation tothe longitudinal axis of the male part so that when the parts arelinked, the respective sides of the beads of the male and female partswhich engage have corresponding angles of slope. Thus the beads on themale part can have sides with angles of slope which make then generallyparallel to the respective sides of the beads on the female part whichthey engage when the parts are linked.

Contrary to initial expectation, this design of bead gives betterresistance against axial separation of the male and female parts of thelinking element under the influence of internal vessel pressure than thereverse relationship of bead side slope.

The male part of the linking element may be sealingly connected orconnectable to the second pressure vessel in the same way in which it isconnected or connectable to the first pressure vessel. Thus, the secondpressure vessel may also have a tubular female part sealingly connectedto an entry port and the tubular male part may be a double endedcomponent which engages the respective female parts of the two pressurevessels at opposite ends.

The linking element is particularly useful for connecting twodecompression chambers so that access to one chamber from the other maybe achieved without loss of pressure. To allow passage of a person fromone chamber to the other, the tubular parts of the linking element needto be of a suitable size. It is convenient to have the linking elementof the same cross-sectional size and shape as at least one of thepressure vessels. In that case, the tubular female part of the linkingelement may be an integral part of the pressure vessel, beingincorporated in, or formed as an extension of the wall of the pressurevessel, preferably at the end of the vessel which is intended toaccommodate the head end of a person contained therein.

The tubular parts of the linking element are preferably of circularcross-section. Each may be formed from a fibre-reinforced plasticsmaterial for strength combined with lightness of weight and a preferredtechnique is to form them by filament winding using resin-impregnatedhigh strength filaments or yarns such as the polyaramid filaments"Kevlar". As mentioned, the tubular female part of the linking elementis formed as an integral part of a pressure vessel according to thisinvention and thus is formed from windings of reinforced filaments oryarns incorporated in a silicone elastomer material.

The linking element described herein may be used to connect a portabledecompression chamber according to this invention to anotherdecompression chamber which may be a fixed unit or another portablechamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a partially sectioned side view of a portable decompressionchamber according to the invention, (without any provision of a linkingelement),

FIGS. 2(a), 2(b), 2(c) and 2(d) are schematic diagrams showing how apatient is placed inside a portable decompression chamber as shown inFIG. 1 with the chamber in the non-pressurised and pressurisedconditions,

FIGS. 3(a) and 3(b) are schematic diagrams showing how the flexiblecasing of a portable decompression chamber folds down for storage andtransportation,

FIGS. 4(a) and 4(b) show a link element for connecting two decompressionchambers according to the invention, and

FIG. 5 shows a part view of the link element of FIGS. 4(a), 4(b) on anenlarged scale and in connecting engagement with two decompressionchambers.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 a decompression chamber 1 comprises a flexiblecylindrical casing 2 of circular cross-section having two end rings 3and 4 moulded into the casing wall. These rings 3 and 4 frame the endsof the cylindrical casing 2, that is the foot end 5 and the head end 6respectively, and provide abutments against which rigid end domes 7 and8 may seat to give a fluid-tight seal when the chamber is internallypressurised. The casing is of a silicone elastomer materialincorporating windings of reinforcing filaments according to theinvention. The end domes 7 and 8 may be of a transparent plasticsmaterial. The end dome 8 which is located at the head end 6 of thecasing 2 has a dome handle 9. The end dome 7 which is located at thefoot end 5 of the casing 2 has a central plate 10 which incorporates adome handle (not shown) and also fittings (not shown) for attaching gashoses for pressurising the chamber 1. Removable chamber handles 11 and12 are attachable to lugs 13 and 14 moulded into the foot and head ends5 and 6 respectively of the casing 2.

Referring to FIGS. 2(a) and 2(b), a patient 15 suffering fromdecompression syndrome is placed on a stretcher 16 which is slid intothe laid out casing 2 of the decompression chamber 1 (FIG. 2(a)). Theend dome 7 is fitted to the foot end 5 of the casing 2 and hoses 17 and18 leading from gas bottles 19 and 20 by way of control box 21 areattached to the hose fittings located in the central plate 10 of the enddome 7. The end dome 8 is then fitted into the head end 6 of the casing2 (FIG. 2(b)).

The chamber 1 is then pressurised by feeding gas into it from the gasbottles 19 and 20 and becomes rigid (FIG. 2(c)). The chamber handles 11and 12 are then fitted, the control box 21 is strapped onto the casing 2and the gas bottles 19 and 20 are carried on the back of one of thebearers 22 and 23 carrying the chamber by the handles 11 and 12 with thepatient 15 inside (FIG. 2(d)).

FIGS. 3(a) and 3(b) show how the flexible casing 2 of the decompressionchamber 1 can be folded down in a concertina-like action from theposition shown in FIG. 3(a) to that shown in FIG. 3(b) for ease ofstorage and transportation.

FIGS. 4(a) and 4(b) show a linking element 24. A cylindrical tubularmale part 25 shown in full line in FIG. 4(a) and outline in FIG. 4(b)has a flexible wall with two series 27 and 28 of alternating beads 29and grooves 30 moulded into its outer surface at both ends.

Each of the two decompression chambers 31 and 32 partly-shown in FIG.4(b) has a tubular cylindrical female part (33 and 34 respectively) ofthe linking element 24 as an extension of the chamber wall. The femaleparts 33 and 34 each have alternating circumferential beads 35 andgrooves 36 on their internal surfaces and these are complementary insize and shape to the beads 29 and grooves 30 moulded externally on themale part 25.

FIG. 5 shows the male and female parts (25, 33 and 34) of the linkingelement 24 in sealing engagement to provide a fluid-tight link betweenthe two decompression chambers 31 and 32. As mentioned earlier, theslope of each side 38 of the circumferential beads 35 on the femaleparts 33 and 34 (as seen in axial cross-section) which face towards therespective entrances of the female parts 33 and 34 in relation to theircommon longitudinal axis is steeper than the opposite sides 37 of thebeads 35. The reverse is of course true for the beads 37 of the beads35. The reverse is are complementary to the intervening grooves 36 onthe female parts 33 and 34.

This shaping of beads nad grooves is the opposite of what one mightexpect to be optimum in preventing relative axial movement apart of themale and female parts of the linking element 24, but in fact is thestronger arrangement.

We claim:
 1. An inflatable decompression chamber of a size when inflatedto accommodate a recumbent person comprising an elongate tubular casinghaving end members for closing the casing to form the chamber, at leastone of the end members being removable to provide access to the interiorof the chamber, the casing comprising a flexible tubular wall of asilicone elastomer material incorporating continuous circumferentialwindings of filaments or yarns within the wall.
 2. An inflatabledecompression chamber as claimed in claim 1 wherein the tubular casingwhen not inflated is capable of being folded down for purposes ofstorage and transportation.
 3. An inflatable decompression chamber asclaimed in claim 1 wherein the tubular casing has an open end closableby the removable end member; said open end being defined by an internalframe which is integral with the wall of the casing and which has asurface facing inwardly of the tubular casing, and wherein the removableend member is a rigid plate which seals against the inwardly-facingsurface of the internal frame under the force of internal pressurewithin the chamber when the chamber is inflated.
 4. An inflatabledecompression chamber as claimed in claim 1 wherein the reinforcingfilaments or yarns comprise 50 to 60 per cent by volume of the tubularwall of the casing.
 5. An inflatable decompression chamber as claimed inclaim 1 wherein the reinforcing filaments or yarns comprise polyaramidfilaments or yarns.
 6. A decompression chamber system comprising aninflatable decompression chamber of a size when inflated to accommodatea recumbent person; said chamber comprising an elongate tubular casinghaving end members for closing the casing to form the chamber, an entryport to the interior of the chamber, one of said end members beingremovable from a position in which the end member closes the entry portso as to provide access therethrough into the chamber, the casingcomprising a flexible tubular wall of a silicone elastomer materialincorporating circumferential windings of filaments of yarns within thewall, a second decompression chamber also having an entry port, and alinking element for linking the respective entry ports of thedecompression chambers in fluid tight relation, wherein the linkingelement comprises a tubular male part and a tubular female part whichare respectively sealingly connected or connectable to the respectiveentry ports of the decompression chambers, the male and female parts ofthe linking element having respective external and internal surfaceswhich are shaped at least in part to correspond and to seal togetherwhen the decompression chambers are linked by the linking element andare internally pressurized, the respective external and internalsurfaces of the male and female parts of the linking element each havingprojections and depressions which engage and hold the surfaces againstsliding axially apart under internal chamber pressure.
 7. Thedecompression chamber system claimed in claim 6, wherein the tubularmale part of the linking element has a wall which is flexible tofacilitate insertion of the male part into the female part, theprojections and depressions on each of the corresponding surfaces of themale and female parts being a succession of circumferential beads andgrooves of which the beads of one part engage in the grooves of theother part.
 8. The decompression chamber system claimed in claim 7,wherein, in axial cross-section, the beads on the female part of thelinking element have sides with different angles of slope in relation tothe longitudinal axis of the female part, with those sides of the beadswhich face towards the entrance to the female part being steeper inslope than opposite sides of the beads, and the beads on the male partof the linking element having sides with different angles of slope inrelation to the longitudinal axis of the male part, with the respectivesides of the beads of the male and female parts which engage on linkingof the parts having corresponding angles of slope.